Perforating guns are commonly used to convey and detonate explosive substances (shaped charges) within wellbores, with the ultimate objective of achieving a hydraulic connection with sought-after deposits of oil and/or natural gas within and/or adjacent to permeable reservoir rocks. Once a promising drilling location has been identified, the creation of wells typically begins with the boring of a hole (i.e. borehole) to reach sought-after deposits of oil and/or natural gas. To prevent collapse of the borehole, a cylindrical casing may be inserted into the borehole. In many situations, cement is pumped into a more or less annular space between the cylindrical casing and the larger cylindrical hole wall to mechanically stabilize the well. While this method improves the stability of the wellbore, it also isolates the inner portions of the casing and the wellbore from the sought-after deposits of oil and/or natural gas.
A perforating gun employs a detonator/initiator and explosive components, which are typically lowered into the casing of the borehole via a wireline or tubing. Operators of the perforating gun at the surface of the wellbore may convey and/or retrieve the gun, or more specifically a series of perforating gun modules. The perforating guns may be conveyed to desired depths within a wellbore in order to detonate explosives to create perforations in the casing, the surrounding cement walls of the wellbore, and the surrounding geological formations. Such perforating gun systems may be used in vertical, deviated, or horizontal borehole shafts. Such perforating gun designs often include structures to protect internal operational components of the gun from the potentially damaging temperatures, vibrations, shock impact, pressures, and fluid-containing environments found within a wellbore, until the actual detonation of explosives occurs. In traditional selectively initiated perforating gun assemblies/systems, the devices include housings, also known as select fire subs, which include pressure bulkheads, which enclose/isolate components such as the pin assemblies, separate detonators, and shaped explosive charges. Examples of perforating guns, their components, and systems which employ such guns are described in U.S. Pat. No. 9,494,021 to Parks et al., U.S. Pat. No. 9,145,764 to Burton et al., and U.S. Pat. No. 9,080,433 to Lanclos et al., each of which are incorporated by reference in their entireties. For the purposes of this application, a perforating gun select fire sub assembly is considered a component of the larger “perforating gun” apparatus. The perforating gun select fire sub assembly often includes the pressure bulkhead structure for housing a firing pin assembly, and other internal components, such as pass-through wiring.
As noted, perforating gun system designs frequently utilize pressure-isolating housing components or bulkhead structures within their select fire sub assemblies for isolating/protecting individual gun modules/components from one another along a chain of gun modules. Such pressure-isolating structures help to prevent inadvertent detonation or detonation interference as a result of exposure to wellbore fluid, pressure, or other conditions of the surrounding wellbore environment. Such pressure-isolating bulkheads may house simple-electrical feed-through or mechanical switches, which enable detonation of the next gun in a line of sequential gun modules.
Use of simple electrical or mechanical switches may mean that only one gun module is electrically connected at any one time to the controller at the wellbore surface, and a specific sequence of events must occur in order to initiate each gun module in a sequence of gun modules. Specifically, the gun modules of these systems are typically detonated from the lowest-most gun module (or end-most gun module farthest from the controller at the surface) to the highest gun module (closest to the controller). An interruption in the firing sequence of sequential gun modules (whether by failure of the simple electrical or mechanical switch) means that an entire firing operation would need to be aborted, adding much cost and time delay to a completion operation. Further, the fact that only one gun module is electrically connected at any one time means that the entire gun string cannot be pre-tested and/or verified to be functional and correctly assembled. Gun failure can only be found when it is too late in the completion operation and the gun operator may not be fully confident that the entire system will eventually work as desired.
In order to provide more reliability and safety to perforating gun assemblies/systems, selective electronic switches have been developed for placement within various components of perforating structures, such as those offered by DynaEnergetics GmbH & Co. KG under the brand DYNASELECT® system, which incorporates a selective electronic switch within a detonator. Such selective electronic switches may include the DYNAENERGETICS® Selectronic Switch. While effective in providing detonation reliability and higher safety levels (i.e. avoiding inadvertent detonation from stray voltage fluctuations or intense RF frequencies which may be common around wellbore operations) such components may add material cost for the operators of such systems when compared to simpler diode type switch systems. Even more advances have been set out in commonly assigned U.S. patent application Ser. No. 15/499,439, entitled “Electronic Ignition Circuit and Method for Use,” filed Apr. 27, 2017, which is incorporated by reference in its entirety.
Others have disclosed arrangements for employing electronic switches in retainer means, for retaining components of a perforating gun within the tubular gun structure. Such specific retainer devices, as those described in U.S. Pat. No. 9,291,040 to Hardesty et al., which is incorporated by reference in its entirety, require that distinct retainers (i.e. threaded pieces) be employed in a perforating gun assembly, thereby imparting potential equipment-specific limitations on operators of such systems. Depending on particular design features, such retainer devices may also expose contained circuitry to environmental conditions of the surrounding wellbore (especially if they are not sufficiently electrically isolated or protected from the wellbore), thereby compromising the reliability or effectiveness of such switches during operation.
It should also be noted that the previously described pressure bulkhead structures of select fire sub assemblies may contain void spaces within their structures. As a result, vibrations, shock-impact, or jarring movement associated with the conveying (pump-down operation) or retrieving of the equipment, or from detonation of gun modules in close proximity on a wireline, can cause components within the pressure bulkhead structures to shift about or contacts to be damaged, potentially leading to a misfire event or damage to the components that may be housed within such pressure bulkhead structures. Such damage may occur even if the components have some fixed connection at one end of the pressure bulkhead.
In view of the disadvantages associated with currently available switching devices for detonating perforating gun modules, there is a need for selective electronic switching devices (and associated circuit boards) which may be easily employed within a long string of perforating gun modules, where the switching devices provide protection from vibrations and environmental conditions of the wellbore. There is a further need for switching devices that may be easily placed within a variety of industry standard gun module equipment design formats, without requiring specific retention constructions.